Safari Omnibar is a SIMBL plugin for Safari that enables a single addressfield/search bar like Google Chrome’s Omnibox. Its still fairly early days, but it works well, and has just been updated to support search shortcuts:
(the search bar is hidden after installation)
To edit keyword searches, right click the address field…
… and then you can then enter the search keywords
This is of course functionality that’s been available in Opera and Firefox, long before Chrome, but this is a great way for folks that prefer Safari to get it.